@BOOK{po1,
  AUTHOR = {Author Red and Author Green and Author Blue and Author Black},
  TITLE  = {Title One},
  DATE   = {2022}
}

@BOOK{po2,
  AUTHOR = {Author Red and Author Green and Author Blue and Author White},
  TITLE  = {Title Two},
  DATE   = {2022}
}

@BOOK{po3,
  AUTHOR = {A. Abraham and B. Brown and C. Cuthbert and D. Abraham},
  TITLE  = {Title One},
  DATE   = {2022}
}

@BOOK{po4,
  AUTHOR = {A. Abraham and B. Brown and C. Cuthbert and D. Darling},
  TITLE  = {Title Two},
  DATE   = {2022}
}

@BOOK{un1,
  AUTHOR = {Neil Smith},
  TITLE  = {Title One},
  DATE   = {2022}
}

@BOOK{un2,
  AUTHOR = {Neil Smith},
  TITLE  = {Title Two},
  DATE   = {2022}
}

@BOOK{un3,
  AUTHOR = {Neil Smith},
  TITLE  = {Title Three},
  DATE   = {2023}
}

@BOOK{un4,
  AUTHOR = {Arthur Smith},
  TITLE  = {Title One},
  DATE   = {2000}
}

@BOOK{un5,
  AUTHOR = {Brian Smith},
  TITLE  = {Title One},
  DATE   = {2000}
}